Mobile phones, personal digital assistants (“PDAs”), digital cameras, MP3 players, and other portable electronic devices utilize light-emitting diodes (“LEDs”), organic light-emitting diodes (“OLEDs”), polymer light-emitting diodes (“PLEDs”), and other SST devices for backlighting. SST devices are also used for signage, indoor lighting, outdoor lighting, and other types of general illumination. FIG. 1A, for example, is a partially schematic cross-sectional view of a conventional SST device 10a. The SST device 10a includes a carrier substrate 20 supporting an LED structure 12 that has an active region 14 (e.g., containing gallium nitride/indium gallium nitride (GaN/InGaN) multiple quantum wells (“MQWs”)) between N-type gallium nitride (“N-GaN”) 16 and P-type gallium nitride (“P-GaN”) 18. A first contact 22 is on the P-type GaN 18 and a second contact 24 is on the N-GaN 16 such that the first and second contacts 22 and 24 are configured in a vertical arrangement on opposite sides of the LED structure 12. In other embodiments, the N-GaN 16 and the active region 14 may be recessed to expose the P-GaN 18, and the first and second contacts 22 and 24 can be spaced laterally apart from one another on forward-facing surfaces or backward-facing surfaces of the N-GaN 16 and the P-GaN. In further embodiments, the SST device 10a can include backside contacts, wherein the second contact 24 extends from the back side of the LED structure 12 into the N-GaN 16 and is electrically isolated from the first contact 22, the P-GaN 18, and the active region 14. Electrical power can be provided to the SST device 10a via the contacts 22, 24, causing the active region 14 to emit light.
The SST device 10a can be configured as a “white light” LED, which requires a mixture of wavelengths to be perceived as white by human eyes. LED structures typically only emit light at one particular wavelength (e.g., blue light), and are therefore modified to generate white light. One conventional technique for modulating the light from LED structures includes depositing a converter material (e.g., phosphor) on the LED structure. For example, as shown in FIG. 1A, a converter material 26 can be positioned over the front surface of the LED structure 12. In other conventional SST devices, such as the SST device 10b shown in FIG. 1B, the LED structure 12 can be positioned in a recessed portion 30 of the underlying carrier substrate 20, and the converter material 26 can encapsulate the LED structure 12 to fill the recessed portion 30.
In operation, the LED structures 12 of the SST devices 10a-b emit light having a certain wavelength (e.g., blue light), and the phosphor of the overlying converter material 26 absorbs some of the emitted photons. This absorption promotes the electrons of the converter material 26 to high unstable energy levels, which causes the converter material 26 to emit longer-wavelength photons (e.g., yellow light) when the electrons ultimately relax to their original state. The combination of the emissions from the LED structure 12 and the converter material 26 is designed to appear white to human eyes when the wavelengths of the emissions are matched appropriately. The generated light can be modulated by optional optical features (e.g., encapsulants or lenses 28) positioned over the converter material 26.
In both the LED devices 10a-b shown in FIGS. 1A and 1B, the converter material 26 is directly on the face of the LED structure 12, and therefore the LED emissions (e.g., blue light) must travel completely through the converter material 26 before exiting the SST device 10a-b. This trajectory through the converter material 26 decays the LED emissions, and thereby reduces the light extraction efficiency of the SST devices 10a-b. In addition, the converter material 26 spontaneously emits photons in random directions such that at least a portion of the converter emissions (e.g., about half of the converter emissions) travel inwardly toward the LED structure 12. The inward converter emissions then reflect off of the face of the LED structure 12 at least once before being extracted from the SST devices 10a-b as useful light. Each such reflection dissipates the emissions, and therefore multiple reflections decrease the light-extraction efficiency of the SST devices 10a-b. 
To reduce the effects of the scattered light, the forward-facing surface of the LED structure 12 can be configured to have reflective properties. However, other considerations, such as current spreading, light-extraction efficiency, and electrical characteristics, may lead to sub-optimal reflectivity of the LED structure 12. To reduce reflections off of the face of the LED structure 12, the converter material 26 of the SST device 10b shown in FIG. 1B is configured to disperse the emissions laterally outward from the forward-facing surface of the carrier substrate 20. The surfaces of the carrier substrate 20 underlying the converter material 26 can be configured to have enhanced reflective properties without being bound by the operating constraints of the LED structure 12.
LED devices have also been designed to include a converter material spaced apart from an LED structure, such as the SST device 10c shown in FIG. 1C. The emissions reflected backward from the remote converter material 26 are less likely to hit the face of LED structure 12, and instead reflect off of other surfaces that have enhanced reflective properties. For example, the arrows shown in FIG. 1C illustrate that the emissions can reflect off of the forward-facing surface of the carrier substrate 20 and/or a larger underlying support substrate 21. However, even when the forward-facing surfaces of the substrates 20, 21 include highly reflective materials, the scattering properties of the converter material 26 still result in multiple emission-dissipating reflections before the light exits the SST device 10c. Moreover, the emissions must still pass completely through the remote converter material 26 before exiting the SST device 10c, which further reduces the light extraction efficiency of the SST device 10c. 